There has been known a technique of correcting image distortions using detection results of projection surfaces on which images are projected. As an example of the techniques of detecting the projection surface, there has been disclosed a technique of detecting a screen frame indicating a frame of a projection surface from a photographed image of a projection image projected on the projection surface (refer to Japanese Patent Application Laid-open No. 2010-044255).
Japanese Patent Application Laid-open No. 2010-044255 discloses that three-dimensional coordinates of a plurality of measurement points formed by a measurement pattern on a projection area are measured, a stepped area including a step on the projection area is detected from the photographed image using the three-dimensional coordinates of the measurement points, and the screen frame is detected from the stepped area. In Japanese Patent Application Laid-open No. 2010-044255, a distortion of image data serving as a projection target is corrected on the basis of the shape of the screen frame.
It is, however, conventionally difficult to correct the distortion of the projection image with high accuracy, because the projection surface is not detected with high accuracy due to the influences of environmental conditions in some cases.